Hello.
You could add a simple invisible object (like a box) without physics collision as a component into an enemy blueprint, and put the enemy in the center of the invisible object. The size of the invisible object will represent enemy’s detection range. Make sure the invisible object will always generate overlap events when intersected with the protagonist. Create a variable called, for example “Detected”, and set it to true if protagonist is overlapping the invisible object and at the same time isn’t located in a place where he can hide. If “Detected” is true, enemy should perform actions tied to protagonist detection, if “Detected” is false, enemy ignores protagonist.